This Corrosion
by ChosenOfAshurha
Summary: The vampire Jim Moriarty takes a peek into John's mind, and sees a beautiful challenge- he's consumed with the need to corrupt that purity, to let the darkness out, to watch John come undone. Written for a prompt on the Johniarty tumblr.


_This is a turn-up, isn't it? _

Sherlock, the person he'd fixated on for so long, that impossible thorn in his side, had gone and gotten himself a pet. And, if he was being honest with himself, a damned good one. Muscular, if a little short, a bit worse for wear… cute as he was, that wasn't what drew the vampire to him. It was his mind. For an average man, he was fairly bright- a doctor must be, after all. He was so pure, so clean, a bastion of honor and duty.

Except for those little black patches scattered throughout. Hints of something dark, some potential locked away inside. _From his days in the army, _Jim thought, staring up at the window leading to the doctor's room.

He'd been thinking about him since Bart's, a quick mental probe that had piqued his interest. _I'm going to make you mine, Doctor Watson. I'm going to let the darkness out and watch you change, and it's going to be beautiful. _

Getting into the room was no problem, not for him. He was, after all, the greatest criminal in the world, for good reason. Up the wall, through the window, and he was beside the doctor's bed. John was laying on his back, one hand under his pillow, the other crossed over his chest. _He's not so bad to look at, if you're into plain. Never expected Sherly to be into that. _

Jim leaned over him, smiling a rather predatory smile as he brushed his fingers across his brow. "I'm going to ruin you, Doctor Watson. I'm going to make you mine." John jolted awake, the hand under the pillow coming up with a gun.

"Who are you, and how the hell did you get in here?!"

Jim's black eyes flashed in the darkness. "Johnny Boy, put the gun down." It took a fair amount of will for him to overpower John's mind, but soon he was setting the weapon on the nightstand. "Good, good. You're so strong, Johnny. I like that. We're going to have fun tonight." He licked his lips and tilted his chin down. _I wonder how far I can get you to go. I wonder how badly I can make you want me. _

"Do Daddy a favor and take off your shirt."

Funny. That one took less work. John pulled off his loose tee, revealing the puckered scar on his left shoulder. Jim made an appreciative sound as he raked his eyes over the doctor's skin. "Well, well, well… Look at you, Doctor Watson. Tell me, is this where you were shot?" He reached forward and brushed his fingers against the scar. John let out a small noise.

"Oh? Now what was that?"

He repeated the action, adding a little more pressure and pinching ever so slightly. There was no mistaking it- that was a moan. Jim chuckled and moved to kneel beside the doctor. Their eyes remain locked. _Alright, Johnny, let's see what's in that mind of yours. _Jim pushed forward with his power. It was hard, at first, pressing into John's mental fortifications. He was surprisingly guarded for a man so in the dark about the true nature of the world. _Things like me aren't supposed to exist. Got something to hide, doctor? _

With a final shove of will he slipped into John's mind. It was just as bright as he remembered, the dark hollows hidden out of his current line of sight- but not for long, no, never for long. Jim decided to make a few more.

"Johnny," he said in a sing-song tone. "I want you to picture me. Innocent, clumsy Jim, from IT. Can you do that for Daddy?"

The image of 'Jim', tight V-Neck and green pants visible above the waist, formed in the blinding space of John's mind. "Oh, you _were _paying attention, weren't you? Liked what you saw?" John nodded slowly, never blinking, utterly mesmerized.

Jim grinned, tracing his fingers around his scar once more. "Oh, I did too. That's why I'm here. I wanted to play. You're much more fun than Sherlock; so moral, so pure… except for the secret thoughts you lock away. I'm going to get to those, you know. I'm going to drain that light from you, Johnny, until you're _mine. _Until Sherlock doesn't want you. Strip me, captain, but don't stop thinking of me."

John began to remove Jim's clothing, starting with the impossibly tight top. As he brushed Jim's pale skin, his body gave a soft groan. "Mmm… I think you're in denial, Johnny, about your preferences. Look at that…" He dropped his hand to John's cotton pyjamas, palming the growing bulge. "Well, well…" The doctor was starting on his trousers next, and Jim stood to give him room. When he was in nothing but his pants, he pinned John against the mattress and rocked his hips, grinding against him.

"Still thinking of me? Good, good… I'm going to let that darkness out, Johnny. I'm going to break your barriers, and I want you to think about what you'd do to me. Visualize it, hold it in your mind. Can you do that for me?"

When the doctor nodded, Jim ran his tongue over his pointed teeth. "Perfect. Such a good boy for me, John." He began to pull John's pyjamas down, letting out a coo of surprise when he discovered the bare flesh beneath. "Commando, captain? I wouldn't expect any less." Manicured fingers slipped down to play with a downy blond hair, watching his cock twitch at the light touches. "Oooooh… Alright, still listening?" John's blue eyes were glazed over, still watching Jim. "It's time to open up those secrets, John. I want you to take a deep breath and lower your barriers. Let mean old Mr. Moriarty see what's so bad."

John's chest expanded slowly, and as he exhaled the dark corners of his mind began to break.

_Smoke, smoke everywhere, and screaming. Gunshots and blood, limbs, and his heart was pounding. His blood was flowing. He was hard. Untrained militia were fleeing from his handful of men. He raises his gun, takes a breath, and fires. Skull explodes. Success. The others fire, taking more down. One of the enemy men steps on a mine and explodes, and he experiences a moment of glee. The battlefield. Glorious. _

The Jim in his mind was cut, bleeding, and smiling. John thought of licking the blood from his skin, sucking it from his wounds, opening more readily.

_Fantasies, dark fantasies. Pain and blood, men and women, screaming in mingled pain and pleasure. Hot wax, whippings, cuts and choking and a powerful need to submit, to be hurt, to worship. Praise, and humiliation, a strange combination of both. Aroused by danger, aroused by death, aroused by high-stress situations. _

"Such a kinky thing, Doctor Watson. You and I could have such a good time… I think we might, before the night is through." Jim leaned in to kiss at his neck, grazing his teeth against his sweat-slicked skin. In John's head, the darkness was spreading slowly, more memories and thoughts leaking through.

_I see him and I want to carve my name across his pale skin. I want to make him mine, mine and no one else's. I want to fuck him until he screams for me, until he can't say anything but my name. I want him to love me, to need me, to be absolutely dependent on me. Sherlock. Mine._

"Dominant _and _submissive? So interesting… More, John. More. Show me _more._"

As more images floated free, Jim began to circle his tongue against John's skin. _I wonder how you taste, Johnny Boy, with the blood of an honorable man. I'm going to stain you, drain you, and leave you craving more. _

"Imagine me, Johnny. Imagine me fucking you up against the freezers at Bart's. Moan for me, Johnny."

Sure enough, the image was there in John's mind.

"Ohn, Jim…"

Jim grinned against his skin and wrapped his fingers around the doctor's length. He began to stroke him lazily, his own erection hard to ignore. "Very good, John. Now, all those dark, possessive thoughts about dear old Sherlock? Make them about _me._"

He watched in delight as, slowly but surely, John began to erase the thoughts of Sherlock. "Yes, John. Want me. Desire me. _Need _Me. Tell me, tell me what you want."

John licked his lips. "Jim. I want Jim. I want you. I want to scratch your skin, bite your flesh, I want to be yours. I want you to fuck me, I want you to hurt me."

The light had started to dim. _Perfect. _

"Do you? Do you want daddy to make you his?"

The doctor nodded, eyes still glassy. "Yes."

Jim grinned and resumed his attention to John's throat. "Then sit back and let dear Jim fix it for you." He began to pump his arm more surely, coaxing soft noises from John's lips. "Mmm, such pretty sounds, Johnny Boy. I think I could get used to this…" John's breath hitched as Jim squeezed him gently, pulsing the muscles in his palms. He rocked against the doctor's thigh, growling as John bared more of his throat. Jim found it hard to wait; John's heart was beating faster, chemicals flooding his system, and it was a beautiful sight. _Hold on tight, Johnny. Daddy's going to fix it. _

He bared his fangs and bit into the skin of John's neck, blood welling from the wounds. Jim sucked with a groan, wrapping his free arm around John's back and pulling him closer. He could feel it running down his chin, dripping onto his bare chest, hot against his cool skin. John let out a gasp, the sound fading into a whine of desperation. With a peek into his mind, Jim could see just how much the soldier liked the soft pain and the nearly intoxicating property of his teeth. There were still plenty of patches of light fighting against the sea of darkness, but they'd come around in time. He'd make sure of it.

Jim drank as he worked his hand, hips rolling as John thrust into his palm. _Going to come for me, Johnny? Going to surrender? I can see how badly you want to. Don't hold back. Give in to me, John. _His legs were trembling, strangled whimpers sounding as he neared the edge. Jim's power enhanced his sensitivity, made him eager, made him _need. _It wasn't long before he was spilling over Jim's hand with a shuddering moan of his name. "O-oh, Jim…"

He pulled back and smeared the excess blood over John's skin. "Such a good boy, John, so good for me. Did you like your reward?" John nodded weakly. "Mmm, I'm glad." He ran his tongue over the puncture wounds, watching his flesh seal itself over. "I think I'll come visit you again tomorrow night, work a little more on that mind of yours. Do you want me to come back, doctor?" Another nod. Jim smiled and licked his stained lips.

"Don't clean up your mess, John. I want you to feel it when you wake up. Don't remember my visit, but dream of me. Think of me. Think of how badly you want me. Can you do that?"

"Yes."

"Very good." Jim pulled his clothes on and touched John's scar once more. "Sleep, Doctor Watson. You'll need your rest." John obeyed, laying down and closing his eyes immediately. Jim severed his glamour and made his way back to the street, grinning smugly.

_And now, I have things to take care of. See you later, Johnny Boy. _He disappeared into the London night without a second glance.


End file.
